1. Field of Invention
The invention is related to a process of manufacturing, filling and closing plastic sacks with dust-like or even granular products as well as of sealing the filled sacks.
2. Description of the Prior Art
Such a device is, for example, known from DE 93 01 355 U. A device for manufacturing, filling and sealing sacks open on one side and preferably provided with side folds made of thermo plastic material is already described here, in which a first welding and cutting station for forming the sack with bottom weld and a second welding station for sealing the sack are available. The filling machines are generally arranged in the FFS (Form, Fill and Seal) category.
While filling dust-like products in machines of the mentioned category through the force of gravity or through free fall, it should be possible to remove the dusty air raised by the falling product from the sack. Removing the air often leads to contaminations in the upper border area of the sack. Conditioned by the contamination with product dust, the sack cannot be sealed securely with the help of the welding that is generally customary in this type of packaging. Moreover, the dust has an adverse effect on the environment and must be removed separately.
Further, filling dusty products according to the described known filling process normally leads to a conspicuously increased product volume or to a clear reduction of the bulk weight, because the product absorbs a lot of air during the free fall. This in turn leads to the condition that considerably more packaging material is used up to fill the product. Moreover, the air must again be removed from the sack, as otherwise it would not be possible to stack or store the sacks.
As the process or air removal is normally very time-consuming, air discharge cannot be undertaken before the sack is sealed. The sack must therefore have a perforation. This has an additional negative influence on the environment, because the fine-grained, dusty products can leak into the atmosphere partially through the perforation in the packaging.
With the passage of time, the volume of the bulk product decreases again. The sack packaging measured on the basis of the packaged bulk volume is conspicuously large. Such filled sacks are very difficult to stack on pallets because they are not stable.
EP 1 459 981 A1 therefore recommends the introduction of the filling branches of a feed element of an FFS machine in the opening of a sack. However, such a device is very expensive from the design perspective.